1. Field of the Invention
The present invention generally relates to metal structures and methods for making the same, and more particularly, to a metal structure defining a circular flanged hole and a method for making the same.
2. Discussion of the Related Art
Circular holes surrounded by flanges are called circular flanged holes. In the customary way of producing flanges surrounding circular holes in metal structures such as deformable metal sheets, it is customary first to pierce or define a preformed hole in the metal structure and then displace portions of the metal structures surrounding the circular hole from a surface of the metal structure to form the flange.
A typical method for making a circular flanged hole in a metal structure such as a sheet or a header plate will now be described. Firstly, a portion of a metal structure is cut out from the metal structure forming a preformed hole in the metal structure. Secondly, a circumferential portion of the preformed hole of the metal structure is deformed and displaced from a surface of the metal structure by a cylinder punch to form a flange. After the two steps, a flanged hole is formed in the metal structure. However, when using the typical method, a collapse portion is generally formed on an edge portion of the flanged hole because of high circumferential tensile deformation caused by the cylinder punch. In addition, if any impurity particles are accidentally adhered to the cylinder surface of the cylinder punch or if the cylinder punch is scratched, the circular flanged hole will be scratched, thus, decreasing the quality of the flanged hole. Furthermore, because the shape of the flanged hole is determined by the cross-section of the cylinder punch, the cross-section of the cylinder punch should be circular, or the shape of the flanged hole would not be circular.
Therefore, a metal structure defining a circular flanged hole is desired in order to overcome the above-described shortcomings. A new method for making a circular flanged hole in a metal sheet is also desired.